188 ON THE EXTINCT MAMMALIA OF 



The first upper jjremolar (figure 2), not existing in the first^described specimens of 

 A. antiquus, is considerably smaller than the succeeding tooth, and its homologue in 

 0. Culbertsoni. It is a reduced representative of the second premolar, but its crown 

 is simpler in not having the strong basal ridge at the postero-internal face. 



The succeeding premolars and the true molars are like those of A. antiquus. 

 (Com23are figures 1, 2, plate XIII, of this work, with figures 5, 6, 10, plate i, of the 

 Ancient Fauna of Nebraska.) 



The first lower premolar, not existing in the first-described specimens of the latter, 

 has a crown like that of the corresponding tooth of Oreodon Culhertsoni. (Figures 1, 

 3, i3late XIII.) 



The second lower premolar resembles that of Oreodon Cidhertsoni, but is propor- 

 tionately smaller. The likeness is greater than in the case of the corresponding 

 tooth of A. antiquus. In this the crown of the tooth forms a broad cone with the 

 outer convex surface separated from the inner sloping and slightly concave surface by 

 an acute border and summit. The posterior border forms a wide festoon, enclosing a 

 cup-like fossa directed inwardly. In A. latifrons, as in 0. Culbertsoni, the crown of 

 the tooth is more trihedral. From near its middle internally there projects a ridge 

 obliquely backward and expanding in the base of the crown. The posterior border 

 of the latter turns inwardly at the base, joins the median ridge, and encloses a 

 lozenge-shaped fossa. 



The last lower premolar (figure 3) resembles the succeeding true molars to such a 

 degree that I at first suspected it was the last of the temporary series of teeth. This, 

 however, appears not to be the case ; all the permanent teeth occujay their 

 functional jDosition, and the last premolar, or what might be supposed to be the last 

 temjjorary molar, is less worn than the first true molar. In A. antiquus the corres- 

 ponding tooth (figure 4) departs more from a likeness to the true molars, in the 

 internal lobes of the crown being proportionately less well-developed, so that they 

 pennit the fore part of the antero-external lobe to be extended inwardly in advance 

 of the antero-internal lobe. 



The lower true molars are identical with those of A. antiquus. (Compare figures 

 1, 3, plate XIII, of this work, with figures 5, 7, 8, 9, plate I, of the Ancient Fauna 

 of Nebraska.) 



The fang of the left inferior canine, retained in the specimen, a^^parently indicates 

 the tooth to have had the same form and relative position as in Oreodon. 



The incisive alveolar border of the lower jaw is nearly all lost, but a portion re- 

 maining on the left side with traces of several alveoli appear to indicate the same 

 number of incisive teeth in Agriochcerus as exist in Oreodon. 



In comparing the cranial specimens originally referred to Eucrotaphus (see Ancient 

 Fauna of Nebraska, page 56, plate vii), and subsequently to Agriochcerus antiquus 



